Use of a light-emitting diode (hereinafter, sometimes referred to as “LED”) attracting attention as a next-generation light source is steadily expanding from a liquid crystal backlight or an automotive lamp to the entire illumination field.
The light source device using an LED chip includes a chip-type LED manufactured by mounting an LED chip on a printed wiring board made from a white copper-clad laminate plate and then resin-encapsulating with a transparent silicone resin or epoxy resin. The light source device above also includes a chip-type LED manufactured by mounting an LED chip in the lead frame part surrounded by a white resin reflector of a composite package in which a lead frame is embedded in the white resin reflector by insert molding, and filling an encapsulating resin in the inside of the reflector. Such a chip-type LED is mounted by soldering on a mother wiring board of an electronic device.
In an LED light source device for the general illumination use, a plurality of high-power LED chips are mounted on one wiring board in many cases and therefore, it is important to efficiently dissipate heat generated in the LED chips and suppress the rise of surface temperature. Because, if the surface temperature of LED chip rises, the life or emission efficiency of the LED chip is reduced. To cope with this, a system of directly fixing an LED chip to a mother wiring board has been proposed as a countermeasure. Furthermore, the mother wiring board itself must have good heat dissipation property and to meet this requirement, use of an insulating metal substrate is being aggressively studied. The insulating metal substrate has a structure where a wiring board having, as an insulating layer, a thermosetting resin layer filled with a heat dissipating filler is stacked on a metal plate. However, since the LED chip is mounted on the insulating resin layer, the heat dissipation property is insufficient.
Accordingly, an LED chip-mounting substrate having more excellent heat dissipation property is demanded. For satisfying this requirement, in Patent Document 1 and Patent document 2, a metal substrate where a metal plate is exposed in the LED chip mounting site (bottom of the cavity) has been proposed.